Review of Green Food Processing techniques. Preservation, transformation, and extraction

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Farid Chemat, Natacha Rombaut, Alice Meullemiestre, Mohammad Turk, Sandrine Périno-Issartier, Anne-Sylvie Fabiano-Tixier, Maryline Vian

To cite this version:

Farid Chemat, Natacha Rombaut, Alice Meullemiestre, Mohammad Turk, Sandrine Périno-Issartier, et al.. Review of Green Food Processing techniques. Preservation, transformation, and ex- traction. Innovative Food Science and Emerging Technologies, Elsevier, 2017, 41, pp.357-377.

�10.1016/j.ifset.2017.04.016�. �hal-01552142�

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DOI: 10.1016/j.ifset.2017.04.016, Journal homepage : http://www.elsevier.com/locate/ifset

Review of Green Food Processing techniques. Preservation, transformation, and extraction

Farid Chemat

^⁎

, Natacha Rombaut, Alice Meullemiestre, Mohammad Turk, Sandrine Perino, Anne-Sylvie Fabiano-Tixier, Maryline Abert-Vian

Université d'Avignon et des Pays de Vaucluse, INRA, UMR408, GREEN Team Extraction, F-84000 Avignon, France

A R T I C L E I N F O

Keywords:

Green Food Processing Preservation Transformation Extraction

Innovative techniques Intensification Bio-refinery

A B S T R A C T

This review presents innovative food processing techniques and their role in promoting sustainable food industry. These techniques (such as microwave, ultrasound, pulse electricfield, instant controlled pressure drop, supercriticalfluid processing) in the frontiers of food processing, food chemistry, and food microbiology, are not new and were already used for > 30 years by academia and industry. We will pay special attention to the strategies and the tools available to make preservation, transformation and extraction greener and present them as success stories for research, education and at industrial scale. The design of green and sustainable processes is currently a hot research topic in food industry. Herein we aimed to describe a multifaceted strategy (innovative technologies, process intensification, bio-refinery concept) to apply this concept at research, educational, and industrial level.

Industrial relevance: Green Food Processing could be a new concept to meet the challenges of the 21st century, to protect both the environment and consumers, and in the meantime enhance competition of industries to be more ecologic, economic and innovative. This green approach should be the result of a whole chain of values in both senses of the term: economic and responsible, starting from the production and harvesting of food raw materials, processes of preservation, transformation, and extraction together with formulation and marketing.

1. Introduction

Food products, such as fruit and vegetables, fat and oils, sugar, dairy, meat, coffee and cocoa, meal and

flours, are complex mixtures of

vitamins, sugars, proteins and lipids,

fi

bres, aromas, pigments, anti- oxidants, and other organic and mineral compounds. Before such products can be commercialized, they have to be processed and preserved for food ready meals and extracted for food ingredients.

Di

ff

erent methods can be used for this purpose, e.g. frying, drying,

filtering, and cooking. Nevertheless, many food ingredients and pro-

ducts are well known to be thermally sensitive and vulnerable to chemical, physical and microbiological changes. Losses of some nutri- tional compounds, low production efficiency, time- and energy-con- suming procedures (prolonged heating and stirring, use of large volumes of water

…

) may be encountered using these conventional food-processing methods. These shortcomings have led to the use of new sustainable

“green and innovative”

techniques in processing, pasteurization and extraction, which typically involve less time, water and energy, such as ultrasound-assisted processing, supercritical

fl

uid extraction and processing, microwave processing, controlled pressure

drop process, and pulse electric

field. The tremendous efforts made on

greening food process can be evaluated through the consideration of books and journals devoted to these aspects (Chemat, Huma, & Khan, 2011).

Food technology under extreme or non-classical conditions is currently a dynamically developing area in applied research and industry. Alternatives to conventional processing, preservation and extraction procedures may increase production efficiency and contri- bute to environmental preservation by reducing the use of water and solvents, elimination of wastewater, fossil energy and generation of hazardous substances. Within those constraints,

“Green

Food Processing

”

has to be introduced on the basis of green chemistry and green engineering:

“Green Food Processing is based on the discovery and design of technical processes which will reduce energy and water consump- tion,allows recycling of by-products through bio-refinery,and ensure a safe and high quality product”

(Fig. 1).

This review presents a complete picture of current knowledge on Green Food Processing techniques for preservation, transformation and extraction as success stories for research, education and at industrial scale. The readers like chemists, biochemists, chemical engineers,

http://dx.doi.org/10.1016/j.ifset.2017.04.016

Received 16 November 2016; Received in revised form 23 February 2017; Accepted 30 April 2017

⁎Corresponding author.

E-mail address:[email protected] (F. Chemat).

Available online 03 May 2017

1466-8564/ © 2017 Elsevier Ltd. All rights reserved.

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physicians, and food technologists even from academia or industry will

find the major solutions identified to design and demonstrate Green

Food Processing on laboratory, classroom and industrial scale to approach an optimal consumption of raw food materials, water and energy: (1) improving and optimization of existing processes; (2) using non-dedicated equipment; and (3) innovation in processes and proce- dures.

2. Instant controlled pressure drop technology

2.1. Process and procedure

DIC

‘Détente Instantanée Contrôlée’, French for Instant Controlled

Pressure-Drop is based on the main principle of the thermodynamics of instantaneity and auto-vaporization processing combining with hydro- intensification

Classical Today’s

US MW

DIC

PEF

CO

₂

Processing yield Processing time Product price

Reduction of Energy

Recycling of by products Product quality HACCP Reduction of Water use

Process safety HAZOP Carbon and water footprint Fig. 1.Green Food Processing: evolution or revolution.

Fig. 2.Schematic representation (a) and photography (b) of DIC process, from experimental conditions (c) to an example of a major macroscopic (d) and microscopic (e) phenomena generated by DIC treatment.

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DOI: 10.1016/j.ifset.2017.04.016, Journal homepage : http://www.elsevier.com/locate/ifset

thermo-mechanical evolution of many biopolymers for food, cosmetic, and pharmaceutical purposes. Developed by Allaf and Vidal (1989), DIC's research began by fundamental studies regarding expansion through alveolation and has targeted several applications in response to issues of control and quality improvement. DIC is considered as a high temperature/high pressure - short time (HTST) treatment and consists of thermo-mechanical processing induced by subjecting the raw material to saturated steam for a short period, and followed by an abrupt pressure drop towards vacuum (about 5 kPa with a rate > 0.5 MPa.s

⁻¹

). Typically, the sample was adjusted to about 30% dry basis and submitted to a

first pressure drop in the treatment vessel to be pre-

conditioned. Then, the sample is subjected to heating under high saturated pressure (up to 1 MPa) at high temperature (up to 180 °C) during a short time (5 to 60 s) and followed by an abrupt pressure drop to vacuum (3–5 kPa,

Δt = 20–200 ms). The abrupt pressure drop (ΔP/

Δ

t > 25.10

⁶

Pa.s

⁻¹

) induces a signi

fi

cant mechanical stress related to instant auto-vaporization of water, an instantaneous cooling of the sample, and swelling phenomenon, causing the rupture of cells and secretion of metabolites through cell walls (Allaf et al., 2011). The purpose of these effects leads to texture change, which results in higher porosity, as well as increased specific surface area and reduced di

ff

usion resistance of the sample. Experimental conditions of DIC extraction allow reduced processing time and the instant reducing temperature drops prevent further thermal deterioration and ensure a high quality of extract (Haddad, Louka, Gadouleau, Juhel, & Allaf, 2001)

DIC equipment is composed of four major components (Fig. 2): (1) an extraction vessel, which is an autoclave with a heating jacket where the sample to be treated is placed; (2) a controlled pressure-drop valve, which ensures a quick and controlled liberation of steam pressure contained in the extraction vessel to the vacuum pump; (3) a vacuum system composed of a vacuum pump and a tank with a volume 50-fold higher than the volume of the treatment vessel; (4) an extract collection trap used to recover condensates; a water ring pump maintains the tank pressure at about 5 kPa. At the beginning, humidi

fi

ed product is placed in the autoclave at atmospheric pressure before vacuum setting. Initial vacuum ensures closer contact of the

fluid heating with the exchange

surface, which enhances the heat transfer in raw material. After closing the valve (between the autoclave and the vacuum tank), the autoclave is

filled with steam up to a processing pressure. After this treatment

time, the controlled pressure-drop valve is instantaneously opened (in < 200 ms), resulting in an abrupt pressure drop inside the treat- ment vessel. After steam release, the atmospheric pressure is returned back inside the reactor.

2.2. Applications in food processing

DIC treatment is employed in several industrial

fi

elds such as food, cosmetic, pharmaceutic in response to issues of control and quality improvement, coupled with reduced energy costs (Allaf & Allaf, 2014).

As shown in Table 1, DIC can be used in various operations such as transformation, preservation, and extraction. For each operation the approach has always induced the integration of phenomena of instan- taneity to intensify the elementary processes of transfer.

The DIC treatment combined to classical hot air drying may be considered as the tool of intensifying the drying when the kinetics of dehydration is particularly low due to difficulty of water transfer through material because of resistance of the natural structure of the material. Recently, Mounir and Allaf (2008) propose an innovative process of 3-stage spray-drying using DIC treatment of powders (sodium caseinates, whey proteins), using saturated steam as a texturing

fl

uid which can permit the modi

fi

cation of powder granule structure, and allows the formation of vacuoles and pores. DIC increases the specific surface area of spray-dried powder and consequently overcomes the problems related to the presence of

fi

ne powder (dustiness). DIC treatment appears to be a good alternative to expand granule powder

of heat-sensitive food such as apple and onion (Mounir, Besombes, Al- Bitar, & Allaf, 2011). After an initial partial drying step, DIC treatment permits the improvement of dehydration kinetic inserting a texturing process allowing the partially dried product to be expanded. The second step of drying (after DIC treatment) is greatly reduced from 6 h (untreated apple) to 1 h in the case of treated-sample. In the case of onion, the e

ff

ective di

ff

usivity is accelerated after DIC treatment (7.56·10

⁻¹⁰

as against 0.46·10

⁻¹⁰

m

²

·s

⁻¹

for untreated sample. At equal water content (100%db.), DIC pretreatment with a pressure comprised between 0.1 and 0.3 MPa and a short heating period of few seconds (5 to 45 s) combined to freezing and thawing allows improvement of drying/rehydration operations for apple with a good preservation of textural properties. DIC is considered as a good alternative process to classical hot air drying and freeze-drying, especially for drying fragile fruit, such as strawberries (Alonzo- Macías, Cardador-Martínez, Mounir, Montejano-Gaitán, & Allaf, 2013).

Furthermore, DIC coupled to hot air drying allows to preserve the nutritional value and bioactive molecules, at optimal DIC conditions (0.35 MPa for 10 s), treated strawberries were richer in anthocyanins and phenolic compounds as compare to other classical drying methods.

DIC is recognized as a process for decontamination, debacterization of foodstu

ff

s. Three patents protect this application (Allaf, Debs-Louka, Louka, Cochet, & Abraham, 1994; Allaf et al., 1998). The treatment allows DIC the elimination of micro-organisms (even in spore forms) through two main mechanisms: a controlled thermal treatment; pres- sure relaxation excessively stressed on microorganisms that cause their explosion (Debs-Louka, Louka, Abraham, & Allaf, 2010). Archeological investigations often renew pieces of wood having spent long periods in water (mostly seawater). The DIC treatment can stop these degrada- tions and stabilize the archeologiocal waterlogged woods originated from different museums (Allaf, Rezzoug, Cioffi, Louka, & Sanya, 1999;

Sanya, Rezzoug, & Allaf, 1998). In the case of thermal treatment for allergen in peanuts, lentil, chickpeas and soybeans proteins, DIC treatment produces a reduction in the overall in vitro IgE binding.

Immunoreactivity of soybean proteins was almost abolished with a treatment at 6 bars for 3 min. Additionally, DIC treatment (0.4 MPa during 25 s) showed decrease in the IgE binding of whey proteins (β- lactoglobulin and

α-lactalbumin) and a greater reduction of the

allergenicity of whey proteins (Boughellout et al., 2015).

DIC pretreatment is considered an efficient method for extraction and texturing from various vegetal materials. Indeed, Mkaouar, Bahloul, Gelicus, Allaf, and Kechaou (2015) showed that DIC texturing on the solvent extraction of polyphenols from olive leaves improves the yield of extraction of 312% and permits generating extract richer in bioactive compounds. Another study has proved that DIC allows enhancing lipid extraction from jatropha and rapeseed seeds without significant modification of fatty acids composition in comparison with conventional Soxhlet extraction (Nguyen Van, 2010). Allaf et al. (2014) have shown that enhancing of lipid extraction by DIC treatment is clearly noticed by calculation of effective diffusivity. DIC process is a good solution for deodorizing and expanse the vegetal matrix in the same time before improving antioxidant extraction from rosemary leaves (Allaf et al., 2013). Expansion of raw material permits a better diffusion of solvent through the material and accelerates the extraction of bioactive compound from 4 h for hydrodistillation to 3 min with DIC.

More recently, DIC was endorsed as a pretreatment for in-situ transes- terification in the case of microalgae. Optimized DIC treatment (P = 0.16 MPa and t = 68 s) allows increasing of 27% in total lipid and > 75% in fatty acids methyl esters yield (Kamal, Besombes, & Allaf, 2014). Additionally, to lipid extraction, it was observed that the residual microalgae allow increasing of lutein extraction. Moreover, DIC allows reducing the energy consumption and manufacturing cost compared to conventional processes of lipid extraction.

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Table1 ExampleofapplicationsandexperimentalconditionsofDIC. ApplicationsMatrixExperimentalconditionsBenefitsReference Transformation Spray-drying (sprayingcouplingtoDICandfinal drying) Milk,sodiumcaseinates Wheyproteinpowders1)Spraying:T=60–180°C,finalpowdershumidity:4and 22%db. 2)DIC:P=0.3–0.7MPa,t=9–25s 3)Drying:50°C,airstream1.2m/sat265Painitial humidity Formationofvacuoles,whichincreasedthe specificsurfacearea Betterfunctionalquality Reducethespecificproblemsofpowder flowability Improvingthekineticsoffinaldrying (Mounir&Allaf,2008) Puffing (HotairdryingandDICtreatment couplingtosnaking)

Onionchips Apple1)Drying:T=40°C,airflow:1m/s,humidity:267Pa 2)DICtreatment:P=0.2–0.6MPa,t=5–55s(apple) P=0.2–0.5MPa,t=5–15s(onion) 3)Hotairdrying(snaking):T=40°C,airflow:1m/s, humidity:267Pa,finalmoisturecontent:5%db.

Greatereffectivediffusivityandinitialstarting accessibility Expandthecompactstructure Vitaminspreservation Low-cost,high-qualitysnakingandpowder

(Mouniretal.,2011) Texturation (pre-dryingcouplingDICandfreezing)Apple1)Pre-dryingat45°C,2m/s,finalwatercontent:30–200% db. 2)DIC:P=0.1–0.3MPa,t=5–45s, 3)Freezing:−30°Cfor600min,afterthawedat4°C

Improvementofdrying/rehydrationoperations Intensifyingtheinternalresistancetowater transfer Goodpreservationoftexturalproperties (BenHajSaid,Bellagha,&Allaf,2015) Swell-drying (couplingDICtostandardhotair drying)

Strawberry GreenMoroccan pepper 1)Partiallyhotairdriedat50°Cuntil18%db., Pvapor=265Pa,airflow:1.2m/s,t=8h 2)DICconditions:P=0.1–0.6MPa;t=10–30s 3)Sameconditionsofhotairdryingbefore Efficienttechniqueforfragilefruit Preservenutritionalvalue Improvequality Decreaseconsumedenergyandcoast

(Alonzo-Macíasetal.,2013) Preservation UHTdecontamination (DICcouplingtohotairdrying)Bacillusstearothermophilus1)InitialDICstage: P=0.7MPa,5mmthickdry,t=3s 2)Heatingstage: T=100–150°C t=5–60s

Destructionofmicroorganismcellwallsandmore specificallyonthesporewall(Debs-Loukaetal.,2010) Conservation (successivepressuredropsdehydration)Archeologicalwaterlogged wood1)Starchimpregnation 2)DICthermaltreatment:T=18–21°C EndofpressuredropT=−1–3°C Smallshrinkage Verygoodsurfaceaspect Initialcolormaintain Lowermoisturecontent Morerapidthanfreeze-drying (Sanyaetal.,1998) Thermaltreatmentforallergen (DIC+solventextraction)Peanuts,lentil, chickpeas,soybeanproteins1)DICtreatment:P=0.3–0.6MPa,t=1–3min,constant initialwatercontentof50%db. 2)Proteinextractionwithn-hexane

Drasticreductioninimmunoreactivity ReductionintheoverallinvitroIgE Timeandenergyreduction Goodalternativetointactproteinsinthe developmentofdifferentfoodproducts

(Cuadradoetal.,2011) Protein'simmunoreactivityMilkP=0.4MPa T=144°C t=25s Pressuredroptowards5kPa,32°C

Enhancetheantigenicityoftreatedcaseins DecreaseintheIgE(Boughelloutetal.,2015) Extraction Diffusion (DIC+solventextraction)Olive(OleaeuropaeaL.)leaves1)DICpretreatmentconditions: P=0.1MPa,numberofcyclesC=1,t=11s 2)Solventextraction DestructionofcellwallsafterDICtexturing Intensificationofsolventextraction

(Mkaouaretal.,2015) Steamextraction(DIC)Oakwood(Quercusalba)chipsP=0.1–0.6MPa,t=30–300st=5min Initialmoisturecontent:20%,thicknessofchips:0.5mmDegradationofwoodcellsandsubsequentrapid liberationofvolatiles Swellingandcreationofalveoleswithinwood microstructure Economyintermsoftimeandenergy (Mellouk,Meullemiestre,Maache-Rezzoug, Allaf,&Rezzoug,2013) Deodorization (DIC+solventextraction)Rosemaryleaves1)DICconditions:P=0.6MPa,timepercycle:6–40s, numberofcycle:1–11 2)Solventextraction

Expansionofrawmaterialinducingabetter extractionofantioxidant Structuralalterationseasedsecondarymetabolite extraction (Allafetal.,2013) (continuedonnextpage)

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DOI: 10.1016/j.ifset.2017.04.016, Journal homepage : http://www.elsevier.com/locate/ifset

2.3. Success story

The technology of instant controlled pressure drop has been generated by Allaf group since 1988, several industrial projects have been developed. Many patents have been

filed since 1993 (Allaf et al.,

1994) and more than twenty PhD theses have treated the subject from di

ff

erent angles. Today, the Allaf group provides research while participating in the design of machinery and the transition from laboratory studies to the industrial stage. The process is operated by ABCAR-DIC Process company, localized in La Rochelle (France). Swell- drying is largely used at industrial scale to produce swell-dried products of > 200 varieties such as apple, banana, strawberry, onion, tomato etc. in the form of cubes, slices and powder that is found in healthy food and unique bands known like

“greedy snacking”, “fruit snacks”

or

“vegetable petals.”

This process was also used for decontamination, dehydration and texturation of many foodstu

ff

s. Furthermore, inter- mediate food products obtained after DIC treatment are used for the development of dehydrated meals or dairy products. The DIC technol- ogy is also largely used for the post-harvest rice processing. The USDA report says that Egypt's rice paddy production in the year May 2012 to April 2013 is expected to rise to 6.37 million tons of dried paddy rice, i.e., 4.5 million tons of dried unbroken white grain DIC rice. In China, many teabags treated by DIC have been commercialized and allow a greater diffusion of tea in water and even in cold water (Allaf & Allaf, 2014).

3. Pulsed Electric Field

Pulsed Electric Field (PEF) treatment, also referred as electropora- tion or electropermeabilization, is a nonthermal process where an external electric

field is applied to a living cell for a very short duration

(from several nanoseconds to several milliseconds) (Fig. 3). The exact mechanism of membrane permeabilization is not precisely understood yet, but it is accepted that electroporation consists of four different stages including (Saulis, 2010): (a) increase of the transmembrane potential of the cytoplasmic membrane due to cell membrane charging by the applied external electric

field, (b) creation of small metastable

hydrophilic pores if a threshold of transmembrane potential is reached (0.2

–

1.0 V), (c) evolution of the number and/or size of the created pores during the PEF treatment, and (d) PEF post treatment stage with leakage of intracellular compounds, entrance of extracellular sub- stances i.e. as irreversible electroporation or pore resealing and integrity recovering of membrane i.e. reversible electroporation.

The effectiveness of cell membranes electropermeabilization de- pends on several process parameters (electric

fi

eld strength, treatment time, speci

fi

c energy, pulse shape, pulse width, frequency and tem- perature), treatment mode (batch, continuous), configuration of treat- ment chamber (collinear, coaxial and parallel) (Van den Bosch, 2007), physicochemical characteristics of the treated matrix (pH and conduc- tivity), characteristics of the treated cells (size, shape, membrane, and envelope structure) and state (suspension, solid, semi-solid) (Vorobiev & Lebovka, 2009).

PEF is a promising green tool in food processing as its opens a wide range of application due to the described phenomenon of cell mem- brane increased permeability or disruption via electroporation. The application can be classified depending on the extent of the applied external electric

field and specific energy (Toepfl, Heinz, & Knorr,

2006). For instance, the application of low electric treatment (E < 2 kV/cm; Q < 5 kJ/kg) is known to induce stress response on the cellular level and is routinely used in molecular biology to gain access to the cytoplasm in order to introduce di

ff

erent molecules. The applications in this

field are rather scarce and are limited to biological

reaction enhancement of vegetable and microbial cells. The improve- ment of mass transfer is generally dependent on higher electric

fi

elds (0.1 < E < 50 kV/cm; 0.4 < Q < 60 kJ/kg). Food preservation due to microbial or enzyme inactivation requires the highest level of

Table1(continued) ApplicationsMatrixExperimentalconditionsBenefitsReference Higherspecificsurfacearea Transesterificationinsitu (DIC+Folchextraction)Microalgae1)DICconditions:P=0.2–0.6MPa,t=20–60s,water content:30and100%db. 2)ModifiedconventionalFolchextraction

Positivelyaffectsporosity,diffusivityandlipid availability Moresaferextraction Quickandeffectiveprocess

(Kamaletal.,2014)

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Fig. 3.Schematic view of a PEF treatment system with a representation of different types of treatment chambers and a brief description of electroporation phenomenon during the electric treatment.

Table 2

Example of applications and experimental conditions of PEF.

Application Matrix Treatment conditions Benefits Reference

Preservation

Inactivation Ringer solution contaminated withB.

subtilisspores

(PEF + heat) 6 < E < 11 kV/cm;

Q < 350 kJ/kg

Inactivation of spores with reduced heat load (Siemer, Toepfl, & Heinz, 2014)

Carrot puree (Chilling + PEF) 0.1 < E < 1.1 kV/cm;

0.15 < Q < 15.58 kJ/kg

Improvement of the stability of vitamin C and reduction of the residual activity of AAO and POD

(Leong, Oey, Clapperton, Aganovic, & Toepfl, 2015) Freezing/thawing Apple; spinach (PEF + impregnation + freezing

+ thawing)

0.58 < E < 0.8 kV/cm; Q: n.d.

Acceleration of freezing/thawing process and comparable texture after defrosting to fresh samples

(Parniakov et al., 2016a; Phoon et al., 2008)

Osmotic dehydration

Apple, carrot (PEF + impregnation) 0.22 < E < 10 kV/cm;

0.15 < Q < 106.7 kJ/kg

Increase of water loss

Solute uptake by the matrix depends on the matrix and operational conditions

(Rastogi et al., 1999; Wiktor et al., 2014)

Convective drying Carrot, red pepper (PEF + hot air drying) 0.5 < E < 2.5 kV/cm;

1.8 < Q < 56.5 kJ/kg^a

Increase of drying rates and color quality (red pepper)

(Gachovska et al., 2008; Won et al., 2015)

Extraction

Diffusion Grape pomace, sugar beet (PEF + extraction by diffusion) 0.6 < E < 3 kV/cm;

Q < 19.4 kJ/kg

Increase of polyphenols and sucrose concentration; selective extraction towards anthocyanins, lower coloration and better filtrability of juices (sugar beet)

(Brianceau et al., 2015; Loginova et al., 2011)

Expression Apple, grape (PEF + extraction by pressing) 0.4 < E < 0.65 kV/cm;

15 < Q < 32 kJ/kg

Increase of juice and polyphenol yield, decrease of juice turbidity and better odor intensity

(Grimi, Lebovka,

Vorobiev, & Vaxelaire, 2009; Turk et al., 2012)

Filtration BSA suspension (PEF + crossflow UF)

E = 4.5 kV/cm, Q: n.d.

Improvement of concentrating rate of protein in retentate and reducing the solute-related resistance to the permeateflux

(Robinson et al., 1993)

Distillation Roses (R. albaL.) E = 25 kV/cm, 10 < Q < 20 kJ/

kg

Increase of oil essential oil yield and possible reduce of distillation time

(Dobreva et al., 2010)

Transformation

Cutting Carrot E = 0.8 kV/cm, Q < 166 kJ/kg Decrease of the cutting force (Leong et al., 2014)

Softening Meat 0.32 < E < 0.48 kV/cm; Q/n.d. Improving meat tenderness (Bekhit et al., 2016)

Frying Potato 0.75 < E < 2.5 kV/cm; Q:

18.9 kJ/kg

Improving potato color and reducing oil uptake after frying

(Ignat et al., 2015) Fermentation S. cerevisiae 100 < E < 6 kV/cm; Q: n.d. Increase of sugars consumption, decrease of

fermentation time

(Mattar et al., 2015)

aData not available in (Won et al., 2015).

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DOI: 10.1016/j.ifset.2017.04.016, Journal homepage : http://www.elsevier.com/locate/ifset

treatment (2 < E < 90 kV/cm; 50 < Q < 44,000 kJ/kg).

3.1. Food preservation

Food preservation (Table 2) is achieved whether by controlling or by inhibiting external contaminants and/or internal biological reactions that could alter the organoleptic and nutritional quality of food. For this, two main strategies are being used: a) applying thermal treat- ments; b) decreasing the water activity of the food matrix to inhibit biological reactions.

Non-thermal PEF processing in liquid foods and beverages preserva- tion has been thoroughly studied as an alternative method to heat preservation. A wide variety of vegetative microorganisms and enzymes have been successfully treated in different food matrices (Griffiths & Walkling-Ribeiro, 2014; Martín-Belloso, Marsellés- Fontanet, & Elez-Martínez, 2014; Terefe, Buckow, & Versteeg, 2015).

Better quality retention in PEF-processed products compared to thermal processing has been observed in many cases. However, PEF has often little or a limited e

ff

ect on enzymes at processing conditions su

ffi

cient for microbial inactivation (50–1000 kJ/kg). At sufficiently high-specific energy input (e.g. > 1000 kJ/kg), PEF causes significant inactivation of enzymes at ambient and mild temperature conditions (Terefe et al., 2015). Commercial PEF treatment systems operate in continuous mode for high productivity. Generally, PEF treated liquid food is packaged after their preservative treatment. A batch treatment mode, in con- ductive plastic material, could also be achieved with comparable levels of inactivation (Roodenburg et al., 2013).

Depending on the required inactivation, target, product composi- tion and initial temperature, it may be advantageous to combine PEF treatment with other treatments (heat, pH, antimicrobial). Such combinations may provide the required lethality at lower

field strength

and with less electrical energy (Álvarez & Heinz, 2007).

Because of their rigid structures, bacterial spores can survive harsh environments for a long period of time. The combination of tempera- ture and electric

fi

elds > 60 °C and 30 kV/cm respectively was e

ff

ective on spore inactivation (Siemer, Aganovic, Toep

fl

, & Heinz, 2015).

The main strength seems to be in PEF ability to affect less the nutritional and sensory properties of food material as compared to thermal treatment. For instance, PEF treated beverages seem to have higher contents of polyphenols, carotenoids and vitamins compared to heat pasteurization (Tokusoglu, Odriozola-Serrano, & Martín-Belloso, 2014).

Freezing is a widespread method for food preservation. Unluckily, such treatment leads to deterioration of food texture and

fl

avors during subsequent transformation operations. The formation, the size of crystals and recrystallization after freezing are the main reasons of the quality loss of frozen foods. Reversible electroporation, due to its transient increase in membrane permeabilization, enables introduction of cryoprotectants into biological cells. This family of molecules prevents crystal formation during freezing. This combination leads to a noticeable acceleration of the freezing/thawing process (Jalté, Lanoisellé, Lebovka, & Vorobiev, 2009; Parniakov, Bals, Lebovka, & Vorobiev, 2016a), increase of freezing temperature and a decrease of the ice propagation rate (Dymek, Dejmek, Galindo, & Wisniewski, 2015). Texture and

firmness of spinach leaves

(Phoon, Galindo, Vicente, & Dejmek, 2008), potato strips were retained by impregnating the material with trehalose (Shayanfar, Chauhan, Toepfl, & Heinz, 2013) and apples with glycerol (Parniakov et al., 2016a).

Dehydration is probably the oldest means for food preservation. The intact cell membranes in food materials represent a highly limiting factor (barrier) to water transport during drying of food matrices. Pore formation during PEF treatment increases cell membrane permeability which enhances the mass transport phenomena. PEF treatment was successfully combined with traditional processes such as osmotic

dehydration, freeze drying, radiant and convective heat. The results are encouraging as the combination of PEF and osmotic dehydration resulted in an increase of water loss and migration of solutes into the food matrix was observed (Rastogi, Eshtiaghi, & Knorr, 1999; Wiktor,

Śledź, Nowacka, Chudoba, & Witrowa-Rajchert, 2014). A significant

reduction of energy consumption and an acceleration of cooling and drying time could also be achieved when apples and potatoes are electrically treated prior to freeze drying without alteration of the dried samples shape (Parniakov, Bals, Lebovka, & Vorobiev, 2016b;

Wu & Zhang, 2014). Similar observations were reported for radiant (Baier, Bußler, & Knorr, 2015) and convective air drying (Gachovska, Adedeji, Ngadi, & Raghavan, 2008; Won, Min, & Lee, 2015). PEF treat- ment was bene

fi

cial to color quality of air-dried products (Won et al., 2015).

3.2. Extraction

Extraction by solvents (diffusion) and force

fields (pressing,filtra-

tion, and centrifugation) is widely used for production of liquid foods and beverages as well as for extraction of molecules of industrial interest. Pretreatments that modify the permeability of the cell mem- branes, such as grinding, heating, or enzymatic treatment, enhance the mass transfer. However, these techniques may require a signi

fi

cant amount of energy and can cause losses of valuable food compounds.

The use of PEF became very popular in this

field as it allows critical

acceleration of the solid

–

liquid extraction. Di

ff

erent technologies of agro-industrial extraction become more selective and less energy consuming if PEF is applied (Vorobiev & Lebovka, 2015).

The combination of PEF and extraction by di

ff

usion has been investigated for improving the extraction of different compounds located on the inside of plant cells, such as colorants (chlorophylls, carotenoids, betalains

…

), sucrose, polyphenols and other secondary metabolites (Puértolas, Luengo, Álvarez, & Raso, 2012). PEF pretreat- ment can be applied for winemaking prior to the macerating fermenta- tion step, the extraction of polyphenols is improved and the wine resulting has di

ff

erent organoleptic (color) attributes (El Darra et al., 2016). The same pretreatment is applied to traditional wine making residues; an enhancement of the selectivity of colorant (anthocyanin) extraction is also highlighted (Brianceau, Turk, Vitrac, & Vorobiev, 2015). PEF application has a large potential for replacement or modification of the conventional thermal technology for sugar extrac- tion from sugar beets. PEF pretreatment assisted

“

cold

”

extraction results in higher concentration of sucrose, lower concentration of colloidal impurities (especially, pectins), lower coloration and better

fi

lterability of juice (Loginova, Loginov, Vorobiev, & Lebovka, 2011).

Traditionally, the increase of the yield in the juice and oil extraction industry has been one of the most important priorities. Gentle techniques that do not cause losses in nutritionally and organoleptic attributes should be used in the procedures to improve the extraction yield. Different plant based matrix was successfully studied for pressure expression combined with PEF pretreatments. Fruit juices (apple, grape

…

) and vegetable oils (olive) yield is signi

fi

cantly increased when moderate PEF treatments are applied before mechanical expression (Vorobiev & Lebovka, 2015). The electric treatment does not induce bad

fl

avors or taste in the oil (Abenoza et al., 2013) and can produce less turbid, significantly odorant and high polyphenols content apple juices (Turk, Vorobiev, & Baron, 2012).

Pulsed Electric Field can also be combined with other mechanical separation operation such as

filtration. The electric treatment helps

reducing the solute-related resistance to the permeate

flux for concen-

trating proteins. Signi

fi

cant improvements in the rate of concentrating the protein in the retentate can be obtained, resulting in reduced membrane surface area requirements for a specific degree of separation (Robinson et al., 1993).

The combination of PEF with extraction methods such as distillation

is also a successive method that leads to an increase of essential oil yield

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and reduces the distillation time (Dobreva, Tintchev, Heinz, Schulz, & Toep

fl

, 2010).

3.3. Transformation

In addition to preservation and extraction applications, other methods were proposed to enhance transformation processes in the latest years. PEF is successfully applied to enhance the mechanical removal of undesired food parts. Skin removal of some fruits (tomato, mango

…

) gave results equal to steam peeling but with low applied energy (Toep

fl

, 2012). The data which are available on this topic are rather scarce.

Several studies have demonstrated interesting e

ff

ects of PEF on softening vegetables and animal tissues. The viscoelastic and textures properties were changed after the electric treatment probably due to loss of turgor pressure (Lebovka, Praporscic, & Vorobiev, 2004). These modi

fi

cations have direct impact on decreasing the cutting force of fruits (Leong, Richter, Knorr, & Oey, 2014) and improving meat tender- ness (Bekhit, Suwandy, Carne, Van de Ven, & Hopkins, 2016).

Several applications in preparation, curing and cooking of meat (McDonnell, Allen, Chardonnereau, Arimi, & Lyng, 2014) and vegetable products have also been proposed (Toepfl, Siemer, & Heinz, 2014). For instance, the application of moderate PEF treatment to potatoes improves its color and reduces oil uptake after frying (Ignat, Manzocco, Brunton, Nicoli, & Lyng, 2015).

Low intensity PEF treatment, inducing reversible electroporation, was recently presented as stressing method to promote production of metabolites in vegetables or to accelerate biological reactions (Toepfl et al., 2006). Mattar et al. (2015) showed that the electric treatment prior to fermentation increases fructose consumption up to 3.98 times at the end of the lag phase and 20 h decrease of the overall fermentation time can be achieved compared to control (without electric treatment).

3.4. Success stories

The numbers of applications related to pulsed electric

fields are

constantly increasing. New ideas are being tested in laboratory and at industrial scale as reliable pulse modulators and tum-key systems.

Recently, new PEF equipment manufacturers, such as Elea, Steribeam, Scandinova, and PurePulse, located in Germany, Sweden, and The Netherlands, respectively, have emerged, thus indicating the growing interest of the food industry in the application of the technology. A cooking device Nutri-Pulse® e-Cooker®, commercialized by IXL Netherlands B.V. is advertised as capable of preparing food with help of electroporation and pulse ohmic heating, results in better conserva- tion of the original nutritive value and the original

flavor, color,

structure and taste.

4. Supercriticalfluids

4.1. Principle, process and procedure 4.1.1. Principle

Supercritical

fluids (SCF) represent an alternative to organic sol-

vents in processes using solvents (Badens, 2012). A

fl

uid is considered to be in its critical state when it is both heated above its critical temperature (Tc) and pressurized above its critical pressure (Pc) (Brunner, 2005). The speci

fi

city of SCF relies in their physical proper- ties, which can be modulated by an increase of pressure and/or temperature, beyond their critical values. SCF have a density close to liquids, which induces a solvating power close to liquids. Their viscosity, close to gases and a diffusivity that is intermediary between liquids and gases, leads to an increase of mass transfer between the solute to extract and the SCF. These properties enable adjustment of solvent selectivity of a SCF towards a target compound, which is particularly interesting in the case of extraction.

Fig. 4.Simplified schematic representation of supercritical CO2installation for solid extraction (A) and liquid extraction (B), example of supercriticalfluid lab scale equipment–1 L autoclave (C).

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DOI: 10.1016/j.ifset.2017.04.016, Journal homepage : http://www.elsevier.com/locate/ifset

Supercritical CO

2

(SC-CO

2

) is the

fluid mostly used in SCF processes

(Rozzi & Singh, 2002). Process implementation is eased due to its low critical coordinates (Tc: 31 °C, Pc: 7.38 MPa). Moreover, some of its advantages include non-inflammability, cheapness, abundance and its volatility at atmospheric pressure implies that after depressurization extracts are solvent-free. SC-CO

2

is a non-polar solvent; its solvent power is comprised between the one of pentane and toluene (Lumia, 2011). To enhance solubilization of polar substances, a polar modifier (ethanol, methanol for example) can be added to SC-CO

2

.

4.1.2. Process implementation

Concerning extraction and fractionation, two types of equipment settings can be found. Supercritical

fl

uid extraction (SFE) from solid materials is achieved with autoclaves (industrial units may be com- posed of several autoclaves for semi-continuous processing). Liquid fractionation with SCF is performed with countercurrent columns (for continuous processing).

SCF extraction installations for solid processing are composed of four main parts: (i) a volumetric pump, to ensure a correct pumping of the

fluid, the pump can be preceded by a cooler which brings gaseous

component in a liquid state (ii) a heat exchanger, (iii) an extractor, where pressure is established and maintained by a back pressure regulating valve, (iv) a separator (Fig. 4A and C). Up to three separators can be put in series, to achieve multiple fractioning of the molecules contained in the extracts.

Extraction by SCF from solids is divided in two main steps: the extraction and the separation of the solute from the solvent. To perform SFE, the

fluid has to be brought in its supercritical state. To achieve this,

the

fl

uid is usually sequentially pressurized and heated before entering the extractor. Brought at the desired pressure and temperature, the SCF percolate in the extractor, with an ascending or descending

flux. The

SCF extract the solute contained in the matrix. Separation of the solute from the SCF will be achieved in the separator, where the SCF will turn into a gaseous state, and the solute no longer solubilized in the SCF will be separated by gravity. Extracts are therefore collected at the bottom of the separator. Depending on the equipment, the gas can be recycled by being re-injected in the system, or released to atmosphere.

Fractioning from a liquid feed can be performed in batch mode, where extraction is performed by desorption of a liquid placed on an absorbent using the same equipment as for solid extraction (Benaissi, 2013). In a continuous mode, a countercurrent column is used to selectively recover a solute from the feed (Fig. 4B). Regarding process implementation, the feed is introduced in the middle or on the top of the column, the supercritical phase being introduced at the bottom of the column. The extract to be recovered and the

fl

uid leave at the top of the column and the raffinate (heavier phase) is recovered at the bottom of the column. SCF preparation and regeneration are similar to SFE from solid material.

Apart from solid/

fl

uid or

fl

uid/

fl

uid extraction processes, SCF are used for particle formation process and are the subject of extensive reviews (Jung & Perrut, 2001; Reverchon, 1999; Reverchon & Adami, 2006; Rodríguez-Meizoso & Plaza, 2015). The general concept of two processes is briefly described below:

RESS (Rapid Expansion of a Supercritical Solution). The solute of interest is diluted in a supercritical phase and the resulting mixture is rapidly depressurized through a nozzle. This process has the advantage to produce very

fi

ne solid particles, but its applications are limited by the polarity of the solutes to precipitate (low polarity solutes).

GAS or SAS (Gas or Supercritical

fl

uid Anti Solvent) which concept is to

“

decrease the solvent power of a polar liquid solvent in which the substrate is dissolved, by saturating it with carbon dioxide in supercritical conditions

”

(Jung & Perrut, 2001). This causes the substrate to precipitate or to recrystallize.

Compared to conventional processes, several key advantages result from the use of SCF. Absence or limited solvent consumption (in the case of co-solvent use) leads to production of a solvent-free extract. The depressurization step in supercritical

fluid processes (SFP) enables

limiting the number of unit operations, since no separation or purifica- tion step is necessary. By operating at low temperatures during the whole process, SFP are adapted to production of heat-sensitive biomo- lecules. Additionally, SCP are intrinsically sterile (Badens, 2012).

4.2. Applications in Green Food Processing

Since the 1970s, a great number of applications using SCF have emerged and have been developed at laboratory and pilot scale. In this section, some applications from published studies related to food processing are reviewed, with a special emphasis on those dedicated to transformation, preservation and extraction by SCF. Far from being exhaustive, the examples given, when possible, will be supported by key related reference reviews or papers.

4.2.1. Transformation

Transformation processes can be achieved with the use of SCF, and most of them are related to particle formation processes. Precipitation or crystallization of food compounds can be achieved by SAS-type processes (e.g. carotenoids). To enhance biomolecules properties pre- servation, encapsulation with SCF has been investigated (Cocero, Martín, Mattea, & Varona, 2009; Rodríguez-Meizoso & Plaza, 2015).

RESS and SAS processes have been successfully applied for anthocya- nins and antioxidant encapsulation (Table 3). Process performances are generally evaluated according to particle characteristics (size and morphology), encapsulation efficiency and release of encapsulated compounds in a matrix.

Textural modi

fi

cations of food matrix have been produced by combining extrusion and SCF (Maskan & Altan, 2011; Rizvi, Mulvaney, & Sokhey, 1995). By injecting SC-CO

2

during the extrusion process, the processing conditions are milder than conventional extru- sion (lower shear and starch expansion is possible below 100 °C).

Therefore, torque, equipment wear and heat-sensitive compound degradation can be minimized. Expansion of extrudates can be con- trolled according to the amount of SC-CO

2

injected, improving the structural characteristics of extrudates (Table 3).

Fractioning by SCF is used for aroma fractioning, where waxes (compounds of high molecular weight) can be separated from the volatile fraction or for lipid fractionation from oils (Reverchon, 1997).

Fractioning can be performed after extraction in the depressurization stages through the separators or with a countercurrent column.

Fractional extraction can also enable a selective recovery of compounds (Table 3, Palma, Taylor, Varela, Cutler, & Cutler, 1999).

The use of SCF for micronization of particles for food applications has been described by Weidner (2009). Production of powdered food such as chocolate or lecithin at different particle size can be obtained through RESS, SAS and PGSS (Particle from Gas Saturated Solutions) (Weidner, 2009).

4.2.2. Preservation

Food preservation aims at conserving organoleptic properties and guarantees safety in food consumption. Food deterioration may be caused by several factors such as micro-organisms development and endogenous enzymatic activity. The use of SCF or high pressure gases for preservation by sterilization, for microbial, virus and spore inactiva- tion has been the subject of some extended reviews (Garcia-Gonzalez et al., 2007; Perrut, 2012; Spilimbergo, Elvassore, & Bertucco, 2002).

High hydrostatic pressure has been known to enable sterilization

and pest control (Perrut, 2012), but the required pressure is quite high

e.g. between 2 and 3000 bars (Spilimbergo et al., 2002). Requiring

milder conditions for similar results, the use of SCF appears as a suitable

alternative for food preservation. Early studies reported that relatively

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Table3 Applicationsofsupercriticalfluidsinfoodtransformation,preservationandextraction. ApplicationMatrix(targetmolecule)ProcessingconditionsBenefitsReference Transformation EncapsulationJabuticabaskins (anthocyanins)RESSprocess PCO2:200bars,40°C,co-solvent:EtOH,encapsulationin polyethyleneglycol 79.78%encapsulationefficiency Stabilityofanthocyaninstolightandtemperature,easeof dissolutioninsolvent (Santos,Albarelli,Beppu,&Meireles,2013) Rosemary(antioxidants)SASprocess PCO2:80to100bars,25to50°C,solvent:EtOH,encapsulation inpoloxamers(Pluronic®F88orPluronic®F127)

100%encapsulationefficiency Quickdissolutioninaqueoussolution(1h),increased protectionagainstdegradationfactorsduringdissolution.

(Visentin,Rodríguez-Rojo,Navarrete, Maestri,&Cocero,2012) FractionationOregano,sage,thyme, marigold(essentialoils)Extraction:PCO2:300bars,40°C Fractionationinseparators(S):100bars(S1)and50bars(S2)Separationofwaxesinfirstseparatorandmaximalrecoveryof essentialoilobtainedinsecondseparator(>70%)(Fornari,Vicente,Vázquez,García- Risco,&Reglero,2012) Grapeseed(phenolicandlipid compounds)Fraction1:pureCO2(456bars,35°C,15minstatic,dynamic phase:solventtofeedratio:16.6) Fraction1:CO2+methanol(5:1,v/v)(456bars,35°C, 15minstatic,dynamicphase:solventtofeedratio:16.6)

Fraction1:composedoffattyacids,aliphaticaldehydesand sterols(10.6%yield) Fraction2:phenoliccompounds7.9%yield(catechin, epicatechinandgallicacid).

(Palmaetal.,1999) TexturalmodificationCornandpotato(extrudate production)SCFXprocesswithwheypowder/eggwhiteincorporation.Die temperature:60°C,screwspeed:100rpm,dieCO2pressure: 100to150bars

Enhancedexpansion,reductionofstarchdegradationand homogeneousmicrocellularstructurecomparedtosteam extrudates (Alavi,Gogoi,Khan,Bowman,&Rizvi,1999) WheatflourSCFXprocess,twinscrewextruder,Dietemperature:80°C, screwspeed:300to400rpm,dieCO2pressure:10barsCO2injectionallowedlowerprocessingtemperaturesand reducedlossofthiamine(3to11%against10to16%)and lowerwaterabsorptionindex.

(Schmid,Dolan,&Ng,2005) Crystallization/ precipitationLycopeneSASprocess,PCO2:7to150bars,35to45°C,solvent: dichloromethaneYieldsabove95% Increasingpressureleadstoincreaseofparticlesizeandhigher initialconcentrationleadstosmallerparticles.

(Miguel,Martín,Gamse,&Cocero,2006) Shrimpresidues(astaxanthin)SASprocess,PCO2:100to120bars,35to40°C,solventtofeed ratio:1,solvent:acetone,co-precipitationwithPluronic®F12774%encapsulationefficiency,highercolorpreservation comparedtocrudeextract(Mezzomoetal.,2012) Preservation BacteriainactivationEscherichiacoli(carrot)PCO2:120bars,35°C,10minNondetectablelevels(Galvaninetal.,2014) Listeriamonocytogenes (drycuredham)PCO2:120bars,50°C,25minNondetectablelevels(Galvaninetal.,2014) SporeinactivationAlicyclobacillusacidoterrestris (applejuice)PCO2:80bars,70°C,30minNondetectablelevels(Bae,Lee,Kim,&Rhee,2009) Bacillussubtilis(suspension)PCO2:80bars,35°C,30min(30cycles)Completeinactivation(Spilimbergoetal.,2002) EnzymeinactivationPolyphenoloxidase (redbeet)PCO2:75bars,55°C,30min93%lossofactivity(Liuetal.,2010) Pectinesterase (orangejuice)PCO2:269bars,56°C,145min100%lossofactivity(Balabanetal.,1991) DryingCarrotPCO2:200bars,40°Cto60°C,50minto15min,co-solvent: EtOH(6%mol)Microstructureandshapeconservation,favorablerehydrated texturalproperties(Brown,Fryer,Norton,Bakalis,&Bridson, 2008) Extraction PercolationTomatowastes(lycopene)PCO2:344bars,86°C,200min61%extractionoflycopene(Rozzi,Singh,Vierling,&Watkins,2002) Almond(oil+tocopherols)PCO2:350to550bars,35to50°C,10to30kg/h,maximum recoveryat2to3hofextractionHighesttocopherolenrichmentinoilobtainedinthefirst2hof extraction.Co-extractionoftocopherolandoilfavoredatthe highestpressurestested.

(Leo,Rescio,Ciurlia,&Zacheo,2005) Liquid/liquidextractionSoybeanoil(lecithin)GASCprocess,PCO2:50to65bars,24.85°C,soybeanoil dilutedin95%hexaneEnrichmentof98.6%oflecithininsolidproduct(Mukhopadhyay&Singh,2004) Propolistincture(essentialoil andflavonoid)SASprocess,PCO2:300bars,60°C,optimumtincture concentration:10%mass100%recoveryofflavonoids(Catchpole,Grey,Mitchell,&Lan,2004) PressingCocoanibs(oil)GAMEprocess,PCO2:100bars,100°C,effectivemechanical pressure:500bars87.1%oilrecoveryagainst71.8%oilrecoveryforconventional pressingatthesameexperimentalconditions(Venteretal.,2006) Linseeds(oil)GAMEprocess,PCO2:100bars,40°C,effectivemechanical pressure:100bars30%increaseusingGAMEprocessbycomparingwith conventionalpressingatthesameexperimentalconditions(Willemsetal.,2008) FiltrationCarrotoil(beta-carotene)310bars,40to60°C,ΔP:30to50bars,membranesare nanofiltersPermeateenrichmentinbeta-carotene(from9.4upto 24.2ppm)(Sarradeetal.,1998) GAME:GasAssistedMechanicalExpression,GASC:GasAnti-SolventCrystallization,PCO2:CO2pressure,RESS:RapidExpansionofaSupercriticalSolution,SAS:SupercriticalAnti-Solvent,SCFX:SupercriticalFluidExtrusion.

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DOI: 10.1016/j.ifset.2017.04.016, Journal homepage : http://www.elsevier.com/locate/ifset

mild conditions were sufficient to inhibit the growth and increase the inactivation rate (heat treatment of 50 to 55 °C with 6 bars of CO

2

) (Fraser, 1951; Perrut, 2012). Generally, the microbial inactivation is greatly affected by pressure, temperature, exposure duration and compression/decompression cycles (Garcia-Gonzalez et al., 2007;

Melo Silva et al., 2013; Perrut, 2012; Spilimbergo et al., 2002). The presence of water is reported to increase the bactericidal effect of CO

2

, most probably due to its relationship with pH, where acidic pH tends to favor inactivation (Garcia-Gonzalez et al., 2007; Garcia-Gonzalez et al., 2009). Some other authors investigated the positive e

ff

ect of condensed gases (e.g. CO

2

, N

2

) on microorganisms inactivation. However, it must be underlined that the matrix e

ff

ect plays a major role during the inactivation process (Garcia-Gonzalez et al., 2007; Wei, Balaban, Fernando, & Peplow, 1991). Recent investigations on food matrices (Table 3) report that inactivation can be obtained with moderate conditions (CO

2

pressure between 80 and 120 bars and below 70 °C).

Such conditions enable a complete inactivation or no detectable levels in foods such as carrots, cured ham, apple and orange juice and red beet after treatment.

Enzyme inactivation can be obtained when exposed to SC-CO

2

conditions or dense phase conditions. Reported factors leading to enzyme inactivation are pH lowering and inhibitory e

ff

ect of molecular CO

2

. In that sense, although inactivation can be achieved with others gases, CO

2

is suggested to have a unique role in inactivation (Damar & Balaban, 2006). At very mild conditions (between 1 and 100 bars at temperatures below 60 °C), inactivation of enzymes such as pectin esterase and polyphenol oxidase can be achieved (Damar & Balaban, 2006). It was noted that some enzymes such as lipoxygenase and peroxidase in sucrose solutions required higher pressures for inactivation (100 to 600 bars, below 55 °C) so some enzymes are more pressure-sensitive than others (Hendrickx, Ludikhuyze, Van den Broeck, & Weemaes, 1998; Tedjo, Eshtiaghi, & Knorr, 2000). Early studies report the use of CO

2

micro- bubbles in batch and continuous systems for enzyme inactivation in liquid materials such as fruit juices (Ishikawa, Shimoda, Shiratsuchi, & Osajima, 1995; Ishikawa et al., 1997;

Wimmer & Zarevúcka, 2010).

4.2.3. Extraction

Extraction by SCF is well-known at both academic and industrial level and therefore is the subject of numerous publications. Four types of processes related to extraction are presented in Table 3.

Supercritical extraction of natural products (such as oils and fats, antioxidants, pigments and aromas) by percolation is described in several reviews (Díaz-Reinoso, Moure, Domínguez, & Parajó, 2006;

Herrero, Cifuentes, & Ibañez, 2006; Reverchon, 1997; Reverchon & De Marco, 2006). From literature survey, it can be identified that usually high pressures are required (above 280 bars) for extraction of high molecular weight compounds such as oils. Aromatic fractions such as essential oils are extracted using moderate conditions (pressures from 70 to 200 bars and temperatures from 40 to 60 °C) (Reverchon, 1997;

Sovová, Aleksovsk, Bocevska, & Stateva, 2006). Focus in extraction by percolation is also set on by-product valorization or on the use of SCF for co-extraction of compounds for enhancement of

final product

attributes (Table 3). Liquid-liquid extraction is applied for numerous applications such as concentrated aromas production from beverages and alcohol removal (Brunner, 2005; Macedo et al., 2008), oil fractionation and deodorization (Shimoda et al., 2000; Torres, Torrelo, Señoráns, & Reglero, 2009), and hexane removal from vege- table oils (Eller, Taylor, & Curren, 2004). Processing pressures rarely exceed 300 bars.

Combined processes with SCF have been investigated to increase extraction performances. A process combining pressing and use of gases in a supercritical state (Gas Assisted Mechanical Expression, GAME) has been recently investigated to increase oil extraction yield (Voges, Eggers, & Pietsch, 2008). This process has been successfully applied

on various seeds (cocoa, linseeds, sesame, Table 3). Authors have noticed that pressing was greatly favored by SCF or dense gases, indeed a low mechanical pressure is necessary (around 10 MPa) to increase oil yield from 10 to 20% (all other conditions equal) (Venter, Willems, Kuipers, & Haan, 2006; Willems, Kuipers, & de Haan, 2008). Nano-

fi

ltration coupled to SC-CO

2

extraction for the puri

fi

cation of low molecular weight compounds (1500 g·mol

⁻¹

) was introduced by Sarrade, Rios, and Carlès (1998). This process has been applied to puri

fi

cation of beta-carotene from carrot oil and to fractionation of

fi

sh oil triglycerides. Further developments on combination of membrane technologies and SCF are still on going in the

field of edible oil refining

(Temelli, 2009).

4.3. Success story in the use of supercriticalfluids: industrial production

Industrial processing with SCF has been a reality for several years.

Since early patents on coffee decaffeination or hops extraction in the 1970′s, a great number of industrial units have emerged. In 2009, Perrut estimated that 300 industrial units were using SCF. For super- critical extraction performed on solid materials, the main applications are related to food and perfume industry: aromas and

flavors extraction

(hops, vanilla, ginger, roses

…

), co

ff

ee and tea deca

ff

eination. For example, Maxwell House Co

ff

ee (a division from General Foods) has reported processing 80,000 tons of coffee per year. The plant is equipped with a 60 m

³

extractor and to function in a semi-continuous scale (Benaissi, 2013). The removed ca

ff

eine is further sold to pharma- ceutic or food companies.

5. Microwave extraction

5.1. Process and procedure

Microwave heating results from the dissipation of the electromag- netic waves in the irradiated medium. The dissipated power in a medium depends on the dielectric properties and the local time- averaged electric

fi

eld strength. So, there is a fundamental di

ff

erence between microwave and conventional heating: in conventional heating, heat transfers occur from the heating device to the medium, whereas in microwave heating, heat is dissipated inside the irradiated medium. In contrast with conventional heating, microwave heat transfer is not limited to thermal conduction or convection currents (Fig. 5). In practice, this means that a much faster temperature increase can be obtained. Furthermore, the maximum temperature of the material heated by microwaves is only dependent upon the rate of heat loss and power applied.

Although microwaves create volumetric heating, the

field distribu-

tion is not even throughout the irradiated material. Therefore, the energy is not homogeneously dissipated. The electric

fi

eld distribution depends on the geometry of the heated object and the dielectric properties. For media which readily absorb microwaves, the depth at which power density is reduced to 1/e of original intensity might be a limiting factor.

For more transparent media, the occurrence of standing wave patterns will result in

‘hot spots’

if the power dissipation is faster than the heat transfers to surrounding colder areas. As a general rule a standing wave pattern can occur if multiples of a half wavelength

fit in

the typical dimension (d) of the irradiated object.

Microwave ovens can have monomode or multimode cavity. The monomode cavity can generate a frequency which excites only one mode of resonance. Their use for food processing is limited because the volume has to be extremely small in order to maintain the resonance.

The majority of food heating applications (Edgar & Osepchuk, 2001) use a multimode resonance cavity applicator because it permits large volumes. The incident wave is able to a

ff

ect several modes of resonance, and this superimposition of modes allows the homogeniza- tion of

field.

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Microwaves are only absorbed by dipoles, transforming their energy into heat. Heat transfer advantages of applying microwave power, a non-contact energy source, into the bulk of a material include: faster

energy absorption, reduced thermal gradients, selective heating and virtually unlimited

final temperature. Several processes such as drying,

tempering, thawing, blanching, sterilization, pasteurization, baking and

Fig. 5.(a) A brief description of phenomenon in the cell generated by microwave irradiation, (b) microwave tunnel to temper, reproduced with permission from SAIREM, (c) microwave cooking of desserts in containers, reproduced with permission from SAIREM, (d) microwave tunnel for pasteurization of liquid food, reproduced with permission from MES Technologies, (e) microwave extraction: SFME and MHG, reproduced with permission from Millestone.

Table 4

Example of applications and experimental conditions of MW.

Application Matrix Treatment conditions Benefits Reference

Preservation

Pasteurization Kiwifruit puree P: 1000 W, t: 200 s and P: 900 W, t:

225 s; m: 500 g

Inactivation 90% of peroxidase enzyme Benlloch-Tinoco, Martínez- Navarrete, & Rodrigo, 2014 Thawing Strawberries P: 700 W, t: 10 min, m: 250 g A reduction in processing time,

No influence on the quality indices (color, ascorbic acid and anthocyanins contents)

Holzwarth, Korhummel, Carle, & Kammerer, 2012 Sterilization Palm fruit P: 800 W, t: 2 min Increment in lauric acid (C12: 0),

Highest concentration of vitamin E and carotene content,

Clean technology due to zero water effluent discharge

Cheng, Mohd Nor, & Chuah, 2011

Extraction

MHG Grape juice by-

products

P: 400 W, t: 20 min, m: 400 g Green extraction method,

Efficiency of MHG in the extraction of polyphenols and anthocyanins from grape by-products

Al Bittar, Périno-Issartier, Dangles, & Chemat, 2013 SFME Lavenderflowers P: 500 W, t: 10 min Extraction of essential oils

Short extraction time

Chemat et al., 2006

MHG Rosmarinus

officinalisL.

P: 500 W, t: 15 min Extraction of antioxidants Economy in term of time and energy More safer extraction

Abert Vian, Fernandez, Visioni, & Chemat, 2008

Transformation

Drying bananas P: 400 W, magnetron is « on » for 11 s and « off» for 18 s, m: 86 g.

Creation dried-and-crisp fruits by applying successive cycles of heating and vacuum pulses in a microwave field

Monteiro, Carciofi, & Laurindo, 2016

Baking Cake batter P: 250 W, t: 67 s, m: 30 g of freshly prepared batter

93% reduction in baking time/convective baking Improvement textural properties such as moisture content andfirmness

Highest nutritive value

Megahey et al., 2005

Blanching Brussels sprouts P: 700 W, t: 5 min followed by blanching in boiling water for 2 min.

No deleterious effects on totalflavonoids and ascorbic acid,

Improvement health properties of Brussels sprouts

Vina et al., 2007

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